Information Technology Reference
In-Depth Information
protocols are built on top of TCP/IP, such as FTP (File Transfer Protocol) for
the retrieval of files (Postel and Reynolds 1985), Gopher for the retrieval of
documents (Anklesaria et al. 1993), and SMTP (Simple Mail Transfer Protocol) for
the transfer of mail (Postel 1982). Since one computer might hold many different
kinds of information, IP addresses were not enough as they only identified where a
particular device was on the network. Thus each protocol created its own naming
scheme to allow it to identify and access things on a more fine-grained level
than IP addresses. Furthermore, each of these protocols was often associated (via
registration with a governing body like IANA, the Internet Assigned Numbers
Authority ) with particular ports, such that port 25 was used by SMTP and port 70
by Gopher. With this explosion of protocols and naming schemes, each Internet
application was its own 'walled garden.' Names created using a particular protocol
were incapable of being used outside the original protocol, until the advent of the
naming scheme of the Web (Berners-Lee 2000).
2.2.2
Information Encoding and Content
There is a relationship between a server sending a message - such as a web-
page about the Eiffel Tower - to a client in response to an HTTP request and
certain notions from information theory, however hazy and qualitative. To phrase
informally, information is whatever regularities held in common between a source
and a receiver (Shannon and Weaver 1963). Note that the source and receiver do
not have to be spatially separate, but can also be temporally separate, and thus
the notion of a self-contained 'message' resembling a postcard being sent between
sender and receiver is incomplete if not incorrect. 7 To have something in common
means to share the same regularities, e.g. parcels of time and space that cannot
be distinguished at a given level of abstraction. This definition correlates with
information being the inverse of the amount of 'noise' or randomness in a system,
and the amount of information being equivalent to a reduction in uncertainty. It is
precisely this preservation or failure to preserve information that can be thought of
the as sending of a message between the source and the receiver over a channel,
where the channel is over time, space, and - most likely - both. Whether or not the
information is preserved over time or space is due to the properties of a physical
substrate known as the channel . So in our example, the channel is the fiber-optic or
copper wires that must accurately carry the voltages which the bits consist of. The
message is the physical thing that realizes the regularities of the information due to
its local characteristics , which in this case would be particular patterns of bits being
preserved over multiple channels as they are popped from an electro-magnetic hard-
disk on a server to fibre-optic then over the air via wireless and finally back to the
7 Imagine that your eye color not changing is a message from yourself at 10 years old to yourself
at 70!
Search WWH ::




Custom Search